1. Field of the Invention
The present invention relates to a process for the synthesis of Ziegler-type catalytic solids or solid constituents of the same.
2. Description of the Background
Ziegler-type catalytic solids, which are used in particular as polymerization or copolymerization catalysts of alpha-olefins in polymers having high molecular weights, are active solids produced when at least one compound of a transition metal belonging to Groups IV to VIII of the Periodic Table of Elements, especially a chloride, oxychloride, or alcoholate of a metal such as titanium, vanadium, zirconium, or chromium, comes into contact with at least one organometallic compound of a metal from Groups I to III of the Periodic Table of Elements, e.g., an organoaluminum or organomagnesium compound.
To produce olefinic polymers or copolymers having a low proportion of ash, the alpha-olefins are polymerized or copolymerized using powerful Ziegler-type supported solid catalysts.
These supported catalysts are generally obtained by combining a transition metal such as those mentioned above, for example a titanium compound such as TiCl.sub.4, TiCl.sub.3, or an alkyl titanate or chlorotitanate, with a magnesium compound, especially MgCl.sub.2, or a precursor system of such a product, and possibly an organic compound which is an electron donor and/or a porous substrate of the silica or metallic oxide type, or a precursor system of this porous substrate. The solid products produced from this combination must be activated when used in the polymerization of alpha-olefins by adding catalysts consisting of reducing organometallic compounds, most often organoaluminum or organomagnesium, and, before activation, they may be designated by supported solid compounds of transition metals for supported Ziegler-type catalytic solids.
The operating methods used to synthesize Ziegler-type catalytic solids, whether supported or not, or to synthesize solid constituents of transition metals for these catalytic solids involve, first, the preparation of said catalytic solid or constituent as a suspension in an inert liquid medium, by bringing into contact the precursor ingredients of the catalytic solid or the constituent in said inert liquid medium in one or several steps, each of which is separated from the following one, if required, by filtration and possibly washing of the solid filtration residue and/or drying of the washed residue; next, the catalytic solid or constituent suspension is subjected to filtration and the solid produced by filtration is washed once or several times using an inert liquid for purification purposes and dried, the suspension is taken up or, in a preferred operation, the washed solid is dried and the dried solid is collected. The solid in suspension or the dried solid thus taken up constitutes the Ziegler-type catalytic solid or the transition metal solid constituent of the catalytic solid.
To conduct these various procedures, use is conventionally made of at least one unit composed of an agitated reactive apparatus followed in series by a drying filter; most often, a plurality of these units forms a chain. The placement in contact, in one or several steps, of the ingredients which form the catalytic solid or transition metal constituent in the inert liquid medium in order to produce the suspension is carried out in the agitated reactor or reactors, while the procedures for filtering the suspension, washing the filtered solid, and drying the washed solid are performed in the drying filter or filters, a process thus requiring most often several transfers of material from the agitated reactor or reactors to the associated drying filter or filters, and vice-versa. In addition to long synthesis time, this kind of procedure leads to appreciable losses of material during each transfer from a reactor to the associated filter, and introduces substantial risks of pollution of the catalytic solid thus prepared or of its component. It also entails substantial consumption of solvent, particularly for the various rinsing procedures.
Thus, a need continues to exist for a process for the synthesis of Ziegler-type catalytic solids or solid constituents of the same, which overcomes the above-mentioned drawbacks.